A capacitive type humidity sensor is disclosed in, for example, U.S. Pat. No. 6,580,600. The sensor includes a humidity device, a capacitance of which is variable in accordance with humidity around the device. The above sensor 90 is shown in FIG. 12. The sensor 90 includes a semiconductor substrate 1 having one surface, on which a moisture sensitive portion 92 and a circuit portion 93 are disposed.
In the moisture sensitive portion 92, a silicon oxide film 2 as an insulation film is formed on the semiconductor substrate 1. A pair of electrodes 91a, 91b is formed on the silicon oxide film 2 in such a manner that one of the electrodes 91a, 91b faces and is disposed apart from the other one of the electrodes 91a, 91b. A silicon nitride film 3 as a protection film and a moisture sensitive film 4 are formed on the substrate 1 to cover the electrodes 91a, 91b. The moisture sensitive film 4 is made of material, dielectric constant of which is variable in accordance with moisture change of atmosphere. Accordingly, the capacitance of a capacitor formed between the electrodes 91a, 91b in the moisture sensitive portion 92 is also variable in accordance with the moisture change of the atmosphere.
The circuit portion 93 includes a standard capacitance portion (i.e., a reference capacitance portion) 94 and a CMOS transistor portion 95. The capacitance change of the capacitor between the electrodes 91a, 91b in the moisture sensitive portion 92 is compared with the standard capacitance of the standard capacitance portion 94, and then, the comparison data is processed in the CMOS transistor portion 95. Thus, in the capacitive type humidity sensor 90, the capacitance change of the capacitor between the electrodes 91a, 91b in accordance with the moisture change of the atmosphere is measured so that the moisture of the atmosphere is detected.
The circuit portion 93 having the standard capacitance portion 94 and the CMOS transistor portion 95 and the moisture sensitive portion 92 are integrally formed on the substrate 1 so that the sensor 90 is integrated. Therefore, the dimensions of the sensor 90 are minimized. Further, the sensor 90 can be formed by a conventional semiconductor manufacturing method; and therefore, a manufacturing cost of the sensor 90 becomes lower.
However, when multiple humidities obtained from different sources are detected at the same time, multiple humidity sensors 90 are necessitated for detecting multiple humidities. Accordingly, the dimensions of a sensor system of the humidity sensors 90 and the weight of the sensor system are increased as the number of measurement sources becomes larger. Further, a manufacturing cost of the sensor system becomes higher.